1. Field of the Invention
The present invention relates to a signal wiring board for transmitting many channel signals and to an improved signal wiring board which can suppress a cross-talk between channels during the transmission of such channel signals.
2. Description of the Related Art
FIG. 1 shows a conventional circuit arrangement for simultaneously transmitting a large number of high-speed channel signals over a signal wiring board from transmission section to a reception section. When, in FIG. 1, the respective channel outputs of transmitter circuits 11.sub.1 to 11.sub.3 in a transmission section 11 are transmitted to corresponding receiver circuits 12.sub.1 to 12.sub.3 in the reception section 12, the outputs of the transmitter circuits 11.sub.1 to 11.sub.3 are connected, for the respective channels, to the inputs of the corresponding receiver circuits 12.sub.1 to 12.sub.3 by corresponding signal transmission paths 13.sub.1 to 13.sub.3 having a characteristic impedance Z.sub.0 with respect to ground and a terminating resistor R.sub.t equal in value to the characteristic impedance Z.sub.0 is connected to a corresponding input terminal of the respective receiver circuits 12.sub.1 to 12.sub.3. According to the aforementioned circuit arrangement, it is possible to reduce a reflection in the respective channel of the reception section 12 by the terminating resistor R.sub.t and to perform a better signal transmission. This advantage is also obtained if the number of channels is increased.
A transmission path formation on the aforementioned signal wiring board has a structure as shown in FIG. 2. In the arrangement shown in FIG. 2, a shows a dielectric layer; b, a ground layer and c, a respective signal transmission path formed of a microstrip. This structure poses no problem upon the transmission of a signal of a relatively low frequency, but cross-talk is increased between the adjacent transmission paths due to the transmission of a high-speed signal on a high-density packaged board. That is, if a distance S between the signal transmission paths is narrowed, electric lines of force are created between the adjacent transmission paths, thus increasing cross-talk there. A degraded signal on transmission results. This degradation is prominently produced upon the transmission of a high-speed signal. For this reason, the transmission of a high-speed signal as well as the implementation of a high-density unit becomes difficult on the conventional structure.
For the conventional signal wiring board as set forth above, it has been difficult to suppress cross-talk which is increased due to the transmission of a high-speed signal as well as the implementation of a high density unit.